Photoperiodic after-effects occurred in 2 short-day species (Cosmos bipinnatus, C. sulphureus) and 4 long-day species (Rudbeckia hirta, Matricaria parthenoides, Centaurea cyanus, Coreopsis tinctoria). The induction photoperiods were begun 28 days after planting, and ranged in number from 1 to 20 or 30. At all other times the plants were kept under photoperiods not favorable for initiation of flower primordia. Cosmos bipinnatus plants exposed to 12 or more short photoperiods bloomed abundantly, and some anthesis occurred on plants exposed to 5-11. Although C. sulphureus plants (Orange Flare var.) retained continuously under long photoperiods bloomed sparsely, abundance of bloom increased with the number of short induction photoperiods. R. hirta, M. parthenoides, C. cyanus, and C. tinctoria bloomed sparsely after exposure to minima of 17, 10, 10, and 18 long photoperiods, respectively. In R. hirta stem elongation was inhibited by short photoperiods, even in the plants which bloomed, but in the other long-day species such inhibition was not universal and only plants with elongated stems bloomed. The short photoperiods retarded growth in all 6 spp. In Matricaria, plants retained continuously under short photoperiods reached a height of only 1.5 cm. and soon died, while those exposed to even 1 long photoperiod thrived. Reproductive-vegetative interphases occurred in 2 spp. only. "Vegetative flowers" developed on R. hirta, and highly modified bracts and flower heads on C. bipinnatus. Reversion to vegetative growth occurred in the latter species, one plant exposed to 5 short photoperiods making a double reversal.